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Electronic applications have expanded to encompass a variety of materials. In particular, allotropes of carbon interest researchers for their electronic applications. Knowledge of carbon allotropes and their applications has expanded significantly since the discovery of C60 Buckminsterfullerene in 1985, the discovery of multi- and single-walled carbon nanotubes in the early 1990s, and the isolation of graphene in 2004. Single-walled carbon nanotubes (SWNTs) have the potential to bring next-generation electronic devices to fruition. Such devices could be flexible, conformable, and inexpensive. SWNT-based electronics are promising for chemical and biological sensing applications, for example, where high carrier mobilities are unnecessary, and material conformity and inexpensive processing are significant advantages. Considerable progress has been made in separating semiconducting SWNTs from metallic SWNTs, enabling SWNT incorporation into semiconducting electronic technologies. Selective sorting of semiconducting SWNTs using π-conjugated polymers is an effective and efficient technique to enrich large quantities of ultra-pure semiconducting SWNTs. Following semiconducting enrichment, SWNTs can be incorporated into electronic devices. This thesis focuses on the enrichment of semiconducting SWNTs via conjugated polymer extraction and incorporating the resulting polymer-SWNT dispersions into thin-film transistors (TFTs). Novel copolymers were investigated for their capacity to selectively sort and disperse large-diameter sc-SWNTs synthesized using the plasma torch technique. Absorption and Raman spectroscopy were employed to monitor the efficacy of the conjugated polymer extraction procedure. Following enrichment, the polymer-SWNT dispersions were incorporated into TFTs. The interaction between the conjugated polymer and the SWNT and the conjugated polymer and dielectric was an essential component of TFT optimization. Furthermore, the procedure of sorting and dispersing sc-SWNTs is investigated for its effect on TFT performance and was another component of TFT optimization. TFTs were electrically characterized in terms of carrier mobility, threshold voltage, hysteresis, and current on/off ratio. The film morphology of the SWNT TFTs was also investigated. Atomic force microscopy and Raman mapping were used to provide insight into the nanometre and micrometre scale film morphology, respectively.

Carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) are carrying great promise as two important constituents of future multifunctional materials. Originating from their minimal defect confined nanostructure, exceptional thermal and electrical properties have been reported for these two allotropic forms of carbon. However, a brief survey of the literature reveals the fact that the incorporation of these species into a polymer matrix enhances its effective properties usually not to the degree predicted by the composite\\textquoteright s upper bound rule. To exploit their full potential, a proper understanding of the physical laws characterizing their behavior is an essential step. With emphasis on the electrical and thermal properties, the following study is an attempt to provide more realistic physical and computational models for studying the transport properties of these nanomaterials. Originated from quantum confinement effects, electron tunneling is believed to be an important phenomenon in determining the electrical properties of nanocomposites comprising CNTs and GNPs. To assess its importance, in this dissertation this phenomenon is incorporated into simulations by utilizing tools from statistical physics. A qualitative parametric study was carried out to demonstrate its dominating importance. Furthermore, a model is adopted from the literature and extended to quantify the electrical conductivity of these nanocomposite. To establish its validity, the model predictions were compared with relevant published findings in the literature. The applicability of the proposed model is confirmed for both CNTs and GNPs. To predict the thermal properties, a statistical continuum based model, originally developed for two-phase composites, is adopted and extended to describe multiphase nanocomposites with high contrast between the transport properties of the constituents. The adopted model is a third order strong-contrast expansion which directly links the thermal properties of the composite to the thermal properties of its constituents by considering the microstructural effects. In this approach, a specimen of the composite is assumed to be confined into a reference medium with known properties subjected to a temperature field in the infinity to predict its effective thermal properties. It was noticed that such approach is highly sensitive to the properties of the reference medium. To overcome this shortcoming, a technique to properly select the reference medium properties was developed. For verification purpose the proposed model predictions were compared with the corresponding finite element calculations for nanocomposites comprising cylindrical and disk-shaped nanoparticles. To shed more light on some conflicting reports about the performance of the hybrid CNT/GNP/polymer nanocomposites, an experimental study was conducted to study a hybrid ternary system. CNT/polymer, GNP/polymer and CNT/GNP/polymer nanocomposite specimens were processed and tested to evaluate their thermal and electrical conductivities. It was observed that the hybrid CNT/GNP/polymer composites outperform polymer composites loaded solely with CNTs or GNPs. Finally, the experimental findings were utilized to serve as basis to validate the models developed in this dissertation. The experimental study was utilized to reduce the modeling uncertainties and the computational predictions of the proposed models were compared with the experimental measurements. Acceptable agreements between the model predictions and experimental data were observed and explained in light of the experimental observations. The work proposed herein will enable significant advancement in understanding the physical phenomena behind the enhanced electrical and thermal conductivities of polymer nanocomposites specifically CNT/GNP/polymer nanocomposites. The dissertation results offer means to tune-up the electrical and thermal properties of the polymer nanocomposite materials to further enhance their performance. / Ph. D.

Cost-effective purification and desalination of water is a global challenge. Reverse osmosis (RO), the current method of choice, requires high pressure drops across the membranes in order to achieve acceptably high flow rates. Conventional polymer membranes are limited in their performance by a trade-off between water permeability and water/salt selectivity. Biofilm fouling is another critical problem in RO applications. Recent simulations and experiments suggest that properly functionalized carbon nanotubes (CNTs) can be used to construct RO membranes that have high permeation flux as well as complete ion rejection, and that are resistant to biofilm formation. The objective of this research was to combine zwitterion-functionalized carbon nanotubes with traditional thin film polyamide (PA) to fabricate a novel desalination membrane which has both high permeability as well as selectivity. Zwitterion functional groups in CNTs act as molecular gatekeepers at the entrance of the nanotubes to enhance blockage for salt ions. Functionalized CNTs were oriented on a membrane support by high vacuum filtration. These oriented CNTs were sealed by a polyamide film via interfacial polymerization. Cross-sectional image of the nanocomposite membrane taken by scanning electron microscopy (SEM) showed semi-aligned zwitterion-CNTs on top of a porous support covered by a thin PA film with an overall thickness of approximately 250 nm. When the concentration of zwitterion-CNTs in the membrane increased, the nanocomposite membranes experienced significant improvement in permeation flux while the ion rejection increases slightly or remains unchanged. This indicated that the increased water flux is not due to an increase in nonspecific pores in the membrane, but rather due to an additional transport mechanism resulting from the presence of the functionalized CNTs. Significant increase of flux was also observed in separating cations other than sodium. The separation of the PA skin layer dominated the ion rejection mechanism by size exclusion even when the carbon nanotubes were introduced into the polyamide coating. The zwitterion functional groups exposed at the membrane surface also interacted with the feed water to form a strong hydration layer, which results in improved surface biofouling resistance. The adsorption rate of protein foulants on the nanocomposite membrane surface was significantly reduced compared to the control membrane without CNTs, and the adsorbed fouling layer could be easily removed by flushing with water. After washing, the nanocomposite membrane recovered 100% of the decreased water flux whereas the control membrane only recovered 10% of the decreased flux resulting in a permanent loss of 30% in water permeation. We have therefore demonstrated that advanced materials like CNTs can be synthesized with desired functional groups, and can be embedded into traditional RO membranes to simultaneously resolve the challenge of low flux and surface fouling in the current desalination process. / Ph. D.

Since the last century a lot of effort has been spent trying to analyze damage and crack evolution in solids. This field is of interest because of the many applications that require the study of the behavior of materials at the micro- or nanoscale, i.e. modeling of composites and advanced aerospace applications. Peridynamics is a recently developed theory that substitutes the differential equations that constitute classical continuum mechanics with integral equations. Since integral equations are valid at discontinuities and cracks, peridynamics is able to model fracture and damage in a more natural way, without having to work around mathematical singularities present in the classical continuum mechanics theory. The objective of the present work is to show how peridynamics can be implemented in finite element analysis (FEA) using a mesh of one-dimensional truss elements instead of 2-D surface elements. The truss elements can be taken as a representation of the bonds between molecules or particles in the body and their strength is found according to the physical properties of the material. The possibility implementing peridynamics in a finite element framework, the most used method for structural analysis, is critical for expanding the range of problems that can be analyzed, simplifying the verification of the code and for making fracture analysis computationally cheaper. The creation of an in-house code allows for easier modifications, customization and enrichment if more complex cases (such as multiscale modeling of composites or piezoresistive materials) are to be analyzed. The problems discussed in the present thesis involve plates with holes and inclusions subjected to tension. Displacement boundary conditions are applied in all cases. The results show good agreement with theory as well as with empirical observation. Stress concentrations reflect the behavior of materials in real life, cracks spontaneously initiate and debonding naturally happens at the right locations. Several examples clearly show this behavior and prove that peridynamics is a promising tool for stress and fracture analysis. / Master of Science